This is an open-access article distributed under the terms of the Creative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

Abstract

The title cocrystal, C18H15OP·C6H6O2, belongs to a series of mol­ecular systems based on triphenyl­phosphine P-oxide. The O atom of the oxide group acts as an acceptor for hydrogen bonds from OH groups of two hydro­quinone mol­ecules which lie on inversion centres [OO = 2.7451 (17) and 2.681 (2) Å]. The crystal structure is stabilized by weak C—HO hydrogen bonds, forming a C21(8) chain which runs parallel to the [100] direction.

Acknowledgments

We are grateful to the Instituto de Química Física Rocasolano, CSIC, Spain, for the use of a licence for the Cambridge Structural Database System (Allen, 2002). RMF and JVN also acknowledge the Universidad del Valle, Colombia for partial financial support.

supplementary crystallographic
information

Comment

The title compound, C18H15OP.C6H6O2, belongs to a series of molecular
systems based on triphenylphosphine P-oxide (TPPO) with diverse hydrogen-bond
donors (Fuquen et al., 1992). In order to expand the crystallographic
information of the TPPO complexes, to study the hydrogen bond character of the
complex, and to analize its supramolecular arrangement, the structure
determination of TPPO + hydroquinone (HQ), (I), system was undertaken. The
free HQ molecule in the more stable form at room temperature (Wallwork &
Powell, 1980) and the free TPPO molecule (Al-Farhan, 1992) can be taken as a
reference systems to compare with the structural characteristics of (I). A
displacement ellipsoid plot of the title hydrogen-bonded complex (I), showing
the atomic numbering scheme is given in Fig. 1. The O1 atom of the P-oxide
group of TPPO acts as an acceptor for hydrogen bonds from O—H groups of two
hydroquinone molecules [O1···O2, 2.7451 (17), O1···O3, 2.681 (2) Å and
O1···H25—O2, O1···H26—O3 angles of 175 (2) and 170 (2)° respectively,
(Table 2)]. These two HQ molecules are each disposed about a centre of
symmetry. The title molecule shows a H25—O1—H26 bond angle close to the
right angle, seeking an orientation with the minor repulsion between the rings
of the molecule. The presence of the three centre hydrogen bond at O1 induces
the lengthening of P—O bond length from 1.479 (2) Å in free TPPO molecule
(Al-Farhan, 1992) to 1.5016 (13) Å in (I). Other bond lengths and angles of
TPPO and HQ remain similar in the complex. The title molecules of (I) are
additionally linked by C—H···O hydrogen bonds. Indeed, atom C3 in the
molecule at (x, y, z) acts as a hydrogen-bond donor to
O3iv atom in the molecule at (x, 1 + y, z), so
generating a C21(8) chain (Etter, 1990) which is running parallel to [100]
direction (Fig. 2, Supp.material). Other significant intermolecular hydrogen
bonds are not observed in the crystalline structure.

Experimental

Crystals of the title compound (I), were obtained by slow evaporation of
equimolecular quantities of HQ (1.826 g, 0.017 mol) and TPPO (4.725 g) in 150 ml of dry acetonitrile. After three days, colourless plates of a good quality
suitable for X-ray analysis were obtained. Its melting point is 425 (1) K.

Refinement

All non-hydrogen atoms were identified by direct methods and the positions of
all the hydrogen atoms were obtained from the use of difference Fourier maps.
In the final refinement, all hydrogen atoms were constrained to geometrically
sensible positions with a riding model (SHELX97), C—H= 0.95 Å, and
Uiso(H)= 1.5Ueq(C), apart from H25 and H26, which were
allowed to refine freely.

Figures

An ORTEP-3 (Farrugia, 1997) plot of the title compound with the atomic labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. Ring H-atoms were omitted for clarity. The dashed line indicates a hydrogen bond. [Symmetry code:...

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor
wR and goodness of fit S are based on F2, conventional
R-factors R are based on F, with F set to zero for
negative F2. The threshold expression of F2 >
σ(F2) is used only for calculating R-factors(gt) etc.
and is not relevant to the choice of reflections for refinement.
R-factors based on F2 are statistically about twice as large
as those based on F, and R- factors based on ALL data will be
even larger.